1. Field of the Invention
This invention relates to polymeric plasticizers. More particularly, this invention relates to polyester type plasticizers wherein a portion of the repeating units are derived from diethylene glycol and at least one dicarboxylic acid.
2. Description of the Prior Art
Plasticizers are well known groups of chemical compounds useful for imparting flexibility, processability and other desirable properties to a variety of materials, including but not limited to organic polymers. Plasticizers are particularly useful for organic polymers that are inherently rigid and difficult to process. Widely used polymers of this type are derived at least in part from ethylenically unsaturated halogenated olefins including but not limited to vinyl- and vinylidene halides such as vinyl chloride and vinylidene chloride.
Desirable properties of plasticizers include efficiency, low permanence and compatibility. An efficient plasticizer will impart its desirable properties at a relatively low concentration, typically 50 weight percent or less, based on the total weight of the polymer composition.
Plasticizers are typically classified as monomeric or polymeric. Polymeric plasticizers are preferred for certain applications, because they are typically less volatile and less easily extracted by water, detergents, oil and organic solvents from polymers into which they have been incorporated. In addition to these desirable properties the plasticizer should be compatible with the polymer into which it is incorporated. Incompatibility typically appears as migration of the plasticizer to the surface of the polymer into which it has been incorporated. In addition to adversely affecting the appearance of the polymer and wetting surfaces in contact with the polymer, incompatibility between polymer and plasticizer typically results in a loss of desirable properties such as flexibility.
The preparation of polyesters from adipic acid, 1,2-propanediol and diethylene glycol is described by J. Wang et al. in Huaxue Shijie [(1998) 29(3), pp. 117-120. The use of these polyesters as plasiticizers for polyvinyl chloride or other polymers is not disclosed.
The use of liquid polyesters prepared using diethylene glycol and at least one dicarboxylic acid as polymeric plasticizers is reported in the literature. S. F. Zawadzki [Polym. -Plast. Technol. Eng. (1993) 32(1-2) pp.155-165] reports that although these polyesters are only slightly compatible with polyvinyl chloride, the plasticizing properties exhibited by these polyesters can be utilized by employing them as secondary plasticizers in combination with other known plasticizers for vinyl chloride polymers.
I. A. Sorokina [Plast. Massy (1975) 8, 25-7] reports that the poor compatibility with polyvinyl chloride of polyesters prepared using adipic acid and diethylene glycol can be improved by replacing the hydroxyl end groups of the polymer with xe2x80x94CH2CH2OC(O)CnH2n+1 groups.
The use as plasticizers for polyvinyl chloride of copolymers prepared by reacting diethylene glycol, 1,3-butanediol and either adipic or phthalic acid is described by A. Abdel-Azim in Polymer International, 47 (1998) pp. 303-310.
Polymeric plasticizers prepared using blends of 1,2-propanediol (1) and 2-methylpropane-1,3-diol (2) and aliphatic dicarboxylic acids containing from 6 to 14 carbon atoms are described in U.S. Pat. No. 6,111,004, issued to Keith Biesiada et al. on Aug. 29, 2000. The molar ratios of (1) to (2) used to prepare the polymers is from 1:3 to 3:1 and the polymers contain from 1 to 12 repeating units per molecule.
The present inventors have discovered that a relatively broad class of difunctional alcohols can be used in combination with diethylene glycol and at least one dicarboxylic acid to prepare polyesters that are efficient yet economical primary plasticizers for homo- and copolymers prepared using halogenated olefins such as vinyl chloride.
Preferred embodiments of the present plasticizers exhibit improved physical properties, including low viscosity. Polymer compositions containing these plasticizers exhibit a higher surface energy, lower glass transition temperature and greater low temperature flexibility relative to compositions containing prior art polyesters as plasticizers.
This invention provides liquid polyester plasticizers, wherein the repeating units of said polyester comprise (I) xe2x80x94OCH2CH2OCH2CH2OC(O)R1(O)Cxe2x80x94, and (II) xe2x80x94OR2OC(O)R1(O)Cxe2x80x94, the terminal groups of said polyester are selected from the group consisting of hydrogen, xe2x80x94R3 and xe2x80x94C(O)R4 and are bonded to an oxygen atom, R1 is at least one member selected from the group consisting of a single bond, alkylene containing from 1 to 20 carbon atoms, cycloalkylene, and ortho-, meta- and para-phenylene; R2 is at least one member selected from the group consisting of alkylene, cycloalkylene and oxyalkylene radicals, wherein said alkylene and oxyalkylene radicals contain from 2 to 8 carbon atoms with the proviso that R2 is not xe2x80x94CH2CH2OCH2CH2xe2x80x94 or xe2x80x94CH2CH2CH(CH3)xe2x80x94; R3 and R4 are individually selected from at least one member of the group consisting of alkyl radicals containing from 1 to 20 carbon atoms, cycloalkyl radicals and phenyl radicals; the repeating units of formula I constitute up to 75 percent by mole of the total repeating units in said polyester.
The weight average molecular weights of the present polyesters are typically up to 10,000. The polyesters are useful as plasticizers for rigid organic polymers, particularly for homopolymers and copolymers prepared from at least one halogen-containing olefin. These olefins contain at least one halogen atom and from 2 to 6 or more carbon atoms. Suitable monomers include but are not limited to vinyl chloride, vinylidene chloride, vinylidene fluoride, 1-chloropropene, 1-chloro-2-butene, and tetrafluoroethylene.
The present polyesters are particularly suitable as primary plasticizers for homopolymers and copolymers of vinyl chloride and vinylidene chloride. Polyvinyl chloride and copolymers of vinyl chloride with at least one ethylenically unsaturated compound, such as vinyl acetate, styrene, and maleic and fumaric acids and esters thereof, are preferred for use with the present plasticizers.
The present polyesters are copolymers of diethylene glycol, at least one additional diol and at least one dicarboxylic acid. In addition to being compatible with the polymers into which they are incorporated, preferred embodiments of the present polyesters and polymer compositions containing these polyesters exhibit unexpected desirable properties. The polyesters exhibit a lower viscosity relative to polyesters of similar molecular weight prepared using diols other than diethylene glycol. Polymer compositions containing the present polyesters exhibit a higher surface energy, a lower glass transition temperature, and greater low temperature flexibility relative to compositions containing prior art polyesters.
As discussed in detail in the following paragraphs, the maximum allowable concentration of repeating units derived from diethylene glycol in polyesters that are compatible with halogen-containing polymers such as polyvinyl chloride is inversely proportional to the molecular weight of the polyester. As used in the present specification, xe2x80x9ccompatiblexe2x80x9d implies that at a concentration of 50 parts by weight per 100 parts of polyvinyl chloride the polyester will not exude from a strip molded from this composition under the conditions described in ASTM test D-3291. In the examples forming part of this specification, the test procedure was modified by changing the sample size from 12.7xc3x9725.4 mm. to 25.4xc3x9776.2 mm.
The present inventors have also discovered that in addition to molecular weight the type of terminal unit present in the polyester will also affect the maximum concentration of units derived from diethylene glycol that can be present in a compatible polyester.
For the purposes of the present invention, the weight average molecular weight of polyesters referred to herein as high molecular weight polymers is typically from 5,500 to about 10,000, polymers exhibiting molecular weights from 2,000 to about 5,500 are referred to as medium molecular weight polymers, and those exhibiting molecular weights below 2,000 are considered low molecular weight polymers.
For high molecular weight polyesters, repeating units derived from diethylene glycol can constitute up to about 40 percent of the total of all repeating units when the terminal unit is derived from an alcohol R3OH. The upper concentration of diethylene glycol derived units is reduced to below 30 percent when the terminal unit is derived from a monocarboxylic acid R4C(O)OH. R3 and R4 are as defined hereinbefore.
For medium and low molecular weight polyesters, when the terminal units are derived from a monohydric alcohol, polymers wherein therefore up to 75 percent of the repeating units are derived from diethylene glycol are compatible with polyvinyl chloride. The polyesters of this invention are typically prepared by reacting diethylene glycol with at least one dicarboxylic acid and at least one of the additional difunctional alcohols, also referred to in this specification as xe2x80x9cdiolsxe2x80x9d or xe2x80x9cglycolsxe2x80x9d, that will yield a plasticizer of the present invention. When the terminal group of the polyester is represented by xe2x80x94R3 or xe2x80x94C(O)R4, a monofunctional alcohol R3OH or a monocarboxylic acid R4C(O)OH is included as a reactant. In the preceding formula R3 and R4 individually represent alkyl containing from 1 to 20 carbon atoms, a cylcoalkyl radical or a phenyl radical.
Suitable diols contain from 2 to 10 or more carbon atoms, and can be represented by the formula HOR2OH. In this formula R2 is at least one alkylene, oxyalkylene and/or cycloalkylene radical, with the proviso that it cannot be xe2x80x94CH2CH2OCH2CH2xe2x80x94 (the residue of diethylene glycol), or xe2x80x94CH2CH2CH(CH3)xe2x80x94 (the residue of 1,3-butanediol) because the use as plasticizers of a polyester prepared from a combination of diethylene glycol with 1,3-butanediol is reported in the literature discussed in the prior art section of this specification. These polyesters are therefore excluded from the plasticizers of the present invention.
Preferably R2 is at least one member selected from the group consisting of alkylene containing from 2 to 10 carbon atoms and oxyalkylene containing from 4 to 8 carbon atoms. Preferred diols include but are not limited to ethylene glycol, 1,2-propanediol (also referred to in this specification as propylene glycol), 1,3-propanediol, 1,2-butanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, neopentyl glycol and dipropylene glycol.
A mixture of diethylene glycol and at least one of the diols of this invention is reacted with a substantially equimolar amount of a dicarboxylic acid or a combination of two or more of these acids.
For the purposes of the present invention, the dicarboxylic acid reactant is represented by the formula HO(O)CR1C(O)OH. In this formula R1 represents at least one member selected from the carbon-carbon single bond, alkylene containing from 1 to 20 carbon atoms, cycloalkylene and ortho-, meta- and para-phenylene. R1 is preferably alkylene containing from 2 to 10 carbon atoms or one of the isomeric phenylene radicals, most preferably xe2x80x94(CH2)4xe2x80x94, p-phenylene or a combination thereof.
Useful dicarboxylic acids include but are not limited to oxalic acid, maleic acid, 1,4-butanedioic acid, adipic acid, 1,4-cyclohexanedioic acid and the isomeric phthalic acids.
When it is desired include a monofunctional alcohol R3OH or a monocarboxylic acid R4COOH as a chain terminating reactant, this reactant can be added together with the dicarboxylic acid and diol. Alternatively, the monofunctional reactant can be added following completion of the polymerization reaction.
In the formulae for the monofunctional reactants, R3 and R4 are each at least one member selected from the group consisting of alkyl radicals containing from 1 to 20 carbon atoms, cycloalkyl and phenyl radicals. R3 is preferably an alkyl radical containing from 1 to 12 carbon atoms and R4 is preferably alkyl containing 1 to 12 carbon atoms or a phenyl radical.
Preferred monofunctional alcohols include but are not limited to methanol, ethanol, 1-propanol, 2-ethyl-1-hexanol and isononyl alcohol. Preferred monocarboxylic acids contain at least 6 carbon atoms and include but are not limited to 1-hexanoic, palmitic and benzoic acids.
The relative concentrations of mono- and difunctional reactants in the reaction mixture are determined by the desired molecular weight of the polymer. For the polyesters of this invention the concentration of monofunctional acid and/or alcohol in the reaction mixture is typically from 5 to about 32 mole percent, based on the corresponding difunctional reactant(s).
The diethylene glycol, additional diol(s) and any desired monofunctional reactants are reacted with at least one dicarboxylic acid under conditions typical for the preparation of polyesters. Because esterification is typically an equilibrium reaction, the reaction is conducted at the boiling point of the reaction mixture. Water, the by-product of an esterification reaction using a carboxylic acid rather than a derivative thereof such as the corresponding anhydride, is typically the lowest boiling material in the reactor. Equipping the reactor with a suitable trap, such as a Dean-Stark trap, located below the reflux condenser allows liquid water to be collected and removed from the reaction mixture. Under the law governing equilibrium reactions, removal of a reaction product forces the reaction toward formation of the desired polyester.
Preferably the ratio of the total number of moles of dicarboxylic acid(s) to total moles of diols in the reactor is from 1:0.89 to 1:1.18 and the reaction is conducted under an inert atmosphere such as nitrogen.
The rate of esterification reactions is typically accelerated in the presence of a suitable catalyst. Preferred catalysts include but are not limited to organic titanates such as tetrabutyl titanate, organotin compounds such as dibutyltin oxide and organic sulfonic acids such as p-toluenesulfonic acid.
The course of the polyesterification reaction can be followed by measuring the quantity of water evolved as a by-product and/or by periodically determining the concentration of unreacted hydroxyl and/or carboxyl groups in the reaction mixture. Using laboratory scale equipment a polyesterification reaction conducted in accordance with the present invention typically requires from 10 to 12 hours.
Methods for isolating and purifying polyesters are sufficiently well known and described in the literature that a detailed description of these methods in the present specification is not required. All of the present polyester plasticizers are liquids at 25xc2x0 C. and do not boil below a temperature of about 200xc2x0 C. under a pressure of 10 mm. of mercury. These polymers can be poured from the reactor following removal by distillation under reduced pressure of any unreacted starting materials and lower boiling by-products. If the reaction residue is colored due to the presence of impurities, the color can usually be removed by treatment with a decolorizing agent such as activated charcoal or an oxidizing agent such as hydrogen peroxide.
Ester and polyester type plasticizers are typically blended with halogen-containing polymers such as homopolymers and copolymers of vinyl chloride to improve the flexibility and processability of these polymers. To be effective the concentration of polyester is typically from about 5 to about 150 parts by weight per 100 parts by weight of halogen-containing polymer. At these concentration levels the plasticizer and polymer must be compatible.
Because diethylene glycol is typically less expensive than other diols, replacing repeating units derived from other diols with units derived from diethylene glycol can considerably lower the cost of a polyester plasticizer.
The polyester plasticizers of the present invention are readily blended with polyvinyl chloride or other polymer using known techniques employed to distribute additives uniformly within a polymer matrix. These techniques include but are not limited to the use of mixers, extruders, kneaders and roller mills.
The following examples describe the preparation and evaluation as plasticizers of preferred polyesters of the present invention. These examples should not be interpreted as limiting the scope of the present invention as defined in the accompanying claims.